1.1.4. ROS 2 - WebSocket bridge¶

Another relevant use-case for Integration Service is that of connecting a WebSocket and a ROS 2 application

The examples detailed below addresses the situation of a ROS 2 talker-listener example communicating with a WebSocket client.

1.1.4.1. Requirements¶

To prepare the deployment and setup the environment, you need to have Integration Service correctly installed in your system. To do so, please follow the steps delineated in the Installation section.

Also, to get this example working, the following requirements must be met:

Having ROS 2 (Foxy or superior) installed, with the talker-listener example working.
Having the ROS 2 System Handle installed. You can download it from the ROS2-SH dedicated repository into the is-workspace where you have Integration Service installed:
```
cd ~/is-workspace
git clone https://github.com/eProsima/ROS2-SH.git src/ROS2-SH
```

Having OpenSSL and WebSocket++ installed:

apt install libssl-dev libwebsocketpp-dev

Having the WebSocket System Handle installed. You can download it from the WebSocket-SH dedicated repository into the is-workspace where you have Integration Service installed:
```
cd ~/is-workspace
git clone https://github.com/eProsima/WebSocket-SH.git src/WebSocket-SH
```

After you have everything correctly installed in your is-workspace, build the packages by running:

colcon build

1.1.4.2. Deployment¶

Below we explain how to deploy an example of this communication in both directions allowed.

ROS 2 pub to WebSocket client¶

To enable communication from ROS2 to a WebSocket client, open two terminals:

In the first terminal, source your ROS 2 installation and execute a ROS 2 pub:

source /opt/ros/$ROS2_DISTRO/setup.bash
ros2 topic pub /hello_websocket std_msgs/msg/String “{data: Hello WebSocket}”

In the second terminal, go to the is-workspace folder, source the ROS 2 and local installations, and execute Integration Service with the integration-service command followed by the ros2_websocket__helloworld.yaml configuration file located in the src/Integration-Service/basic folder:
```
cd ~/is-workspace
source /opt/ros/$ROS2_DISTRO/setup.bash
source install/setup.bash
integration-service src/Integration-Service/examples/basic/ros2_websocket__helloworld.yaml
```

Up to this point, the Integration Service should have created a WebSocket server application within the WebSocket System Handle, to listen and handle petitions coming from a WebSocket client.

We will now explain how to simply test the intercommunication between ROS 2 and a demo WebSocket client application, which can be found in websocket.org/echo webpage:

First, under the Location section, connect to the WebSocket server automatically deployed by the Integration Service. To do so, and since the example is being run without SSL security, copy and paste the following URL into the Location field text box, and press Connect:
```
ws://localhost:80
```
After this, you should see two WebSocket messages received automatically, due to the fact that the WebSocket Server hosted in the Integration Service detected an incoming connection: a subscribe operation message for the hello_ros2 topic; and an advertise operation for the hello_websocket topic.
Since the ROS 2 talker to WebSocket client example is being tested, we must first send a subscribe operation request for the hello_websocket topic. To do so, under the Message text box, enter the following and press Send:
```
{"op": "subscribe", "topic": "hello_websocket", "type": "std_msgs/String"}
```

After this, in the Log you should receive the following message from ROS 2:

RECEIVED: {"msg":{"data":"Hello WebSocket"},"op":"publish","topic":"hello_websocket"}

WebSocket client to ROS 2 echo¶

To enable communication from a WebSocket client to ROS 2, open two terminals:

In the first terminal, source your ROS 2 installation and execute a ROS 2 echo:

source /opt/ros/$ROS2_DISTRO/setup.bash
ros2 topic echo /hello_ros2 std_msgs/msg/String

In the second terminal, go to the is-workspace folder, source the ROS 2 and local installations, and execute Integration Service with the integration-service command followed by the ros2_websocket__helloworld.yaml configuration file located in the src/Integration-Service/basic folder:
```
cd ~/is-workspace
source /opt/ros/$ROS2_DISTRO/setup.bash
source install/setup.bash
integration-service src/Integration-Service/examples/basic/ros2_websocket__helloworld.yaml
```

Up to this point, the Integration Service should have created a WebSocket server application within the WebSocket System Handle, to listen and handle petitions coming from a WebSocket client.

We will now explain how to simply test the intercommunication between ROS 2 and a demo WebSocket client application, which can be found in websocket.org/echo webpage:

First, under the Location section, connect to the WebSocket server automatically deployed by the Integration Service. To do so, and since the example is being run without SSL security, copy and paste the following URL into the Location field text box, and press Connect:
```
ws://localhost:80
```
After this, you should see two WebSocket messages received automatically, due to the fact that the WebSocket Server hosted in the Integration Service detected an incoming connection: a subscribe operation message for the hello_ros2 topic; and an advertise operation for the hello_websocket topic.
Since the WebSocket client to ROS 2 echo example is being tested, we must first send an advertise operation request for the hello_ros2 topic. To do so, under the Message text box, enter the following and press Send:
```
{"op": "advertise", "topic": "hello_ros2”, "type": "std_msgs/String"}
```

After this, we can send individual messages from the WebSocket client, using the publish operation:

{"op": "publish", "topic": "hello_ros2", "msg": {"data": "Hello ROS 2"}}

The messages should be shown in the ROS 2 echo terminal.